"The Government will need to be certain that any weapons deployed are under some form of 'ironclad' control".

The Royal Navy argued that officers of the Royal Navy as the Senior Service could be trusted:

"It would be invidious to suggest... that Senior Service officers may, in difficult circumstances, act in defiance of their clear orders".

Neither the Navy nor the RAF installed PAL protection on their nuclear weapons.

The RAF kept their unsafeguarded bombs at airbases until they were withdrawn in 1998.

Bicycle lock key

With the help of Brian Burnell - a researcher into the history of the British nuclear weapons programme who once designed bomb casings for atom bombs - Newsnight tracked down a training version of the WE 177 nuclear bomb at the Bristol Aero collection at Kemble.

Tornado and earlier V-bomber crews trained with these, which were identical in every way to the live bombs except for the nuclear warhead.

To arm the weapons you just open a panel held by two captive screws - like a battery cover on a radio - using a thumbnail or a coin.

Inside are the arming switch and a series of dials which you can turn with an Allen key to select high yield or low yield, air burst or groundburst and other parameters.

The Bomb is actually armed by inserting a bicycle lock key into the arming switch and turning it through 90 degrees. There is no code which needs to be entered or dual key system to prevent a rogue individual from arming the Bomb.